There are a number of high temperature applications where fast and accurate control over fluid flow is needed. One exemplary and very significant application is controlling the boost pressure provided by a turbocharger. Turbochargers affect the air fuel (A/F) ratio combusted in the cylinders of modern internal combustion engines, which includes diesel and natural gas engines. Turbochargers include a compressor for compressing air and a turbine for driving the compressor. The turbine operates off of the exhaust flow exiting the engine. To achieve the most efficient engine performance, the boost pressure of the air delivered into the cylinders must be accurately controlled.
One way to obtain better control over the compressor boost pressure is to control the amount of exhaust flowing through the turbine. This can be done by providing a controlled wastegate valve which closely regulates or modulates the amount of exhaust flowing through the turbine. Design of the controlled wastegate valve must take into consideration the harsh environment in which the valve operates. The wastegate valve may be subjected to exhaust gas temperatures of up to 1400.degree. F. Being in close proximity to the combustion chambers, the wastegate valve also must handle the vibration and heat transfer coming from the engine block.
There are known prior attempts of regulating the exhaust flow through the turbines of turbochargers using pneumatically controlled flow control valves. A typical prior attempt includes the use of a pneumatic actuator for controlling the position of a swing valve or poppet valve. The swing or poppet valve regulates the flow of exhaust through an exhaust bypass in the engine turbocharger. While, pneumatic actuators can be configured to withstand the high temperature environment, they provide a slow response with a significant amount of rotational hysteresis resulting from pressure differentials between the valve and the pneumatic actuator. Furthermore, swing and poppet valves have very high gain characteristics, making precise control impracticable. These factors cause deficient control of the turbo boost pressure. This results in inefficient control of the engine turbocharger and lower efficiency for the combustion engine.
In cool temperature applications, such as throttling ambient temperature air into an engine, there are known electrically actuated butterfly valves. Such electrically actuated butterfly valves typically have a single solid shaft which transfers the rotational output of an electrical actuator to the butterfly valve. These electrical actuators are highly responsive which provides fast and accurate control of the butterfly valve and the low temperature gas which flows therethrough. However, the shaft is an excellent conductor of heat and vibration which would cause overheating and/or failure of the electrical actuator if applied to high temperature applications, such as a wastegate flow control valve for regulating exhaust flow to a turbocharger for example.
There are also known attempts at providing electrically actuated butterfly valves for exhaust braking. For example, U.S. Pat. No. 2,753,147, to Welge, illustrates an electrically actuated on/off butterfly valve for building backpressure against the engine pistons to slow the vehicle when the vehicle is traveling down a steep slope. However, the engine braking valve in Welge would not be suitable for controlling turbo boost pressure in an engine. Welge discloses an on/off type valve that is not continuously variable. Such on/off type valves do not provide the control, responsiveness or accuracy necessary for the desired control of turbo boost pressure. Furthermore, the output shaft of the electrical actuator is disposed along a separate axis spaced parallel to the input shaft of the butterfly valve. Rotation is transferred from the output shaft to the input shaft by a spring, roller and track mechanism which causes the input and output shafts to rotate in opposite directions. This connection between input and output shaft increases the complexity of the valve and allows rotational play between shafts which in turn would decrease the responsiveness and control of the butterfly valve.
Yet, another problem with Welge is that it does not appear to be adapted for the harsher environmental conditions necessary for controlling exhaust flow through an engine turbocharger. In Welge, the butterfly valve is adapted to be mounted between the outlet of the exhaust manifold and the inlet of the exhaust line, which can be further downstream from the engine combustion chamber as compared with the typical location of the bypass in an engine turbocharger. This downstream location is a less harsh environment in terms of temperature and vibration as compared with a typical turbocharger bypass. And therefore it does not suffer from the problems to which the instant invention is directed.